Hydrocarbon isomerization catalyst and process

ABSTRACT

Isomerizable hydrocarbons are isomerized using a catalytic composite comprising a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of a platinum group component, which is maintained in the elemental metallic state during the incorporation and pyrolysis of the rhenium carbonyl component, of a tin component, and of a halogen component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my co-pending applicationSer. No. 68,278 filed Aug. 20, 1979 and issued on Mar. 17, 1981 as U.S.Pat. No. 4,256,566 which is a continuation-in-part of my applicationSer. No. 833,332 filed Sept. 14, 1977 now U.S. Pat. No. 4,165,276. Theteachings of which applications are incorporated herein by specificreference thereto.

FIELD OF THE INVENTION

This invention relates to a catalyst and process for isomerizingisomerizable hydrocarbons including isomerizable paraffins,cycloparaffins, olefins and alkylaromatics. More particularly, thisinvention relates to a process for isomerizing isomerizable hydrocarbonswith a catalyst comprising a combination of a catalytically effectiveamount of a pyrolyzed rhenium carbonyl component with a porous carriermaterial containing a uniform dispersion of catalytically effectiveamounts of a platinum group component, which is maintained in theelemental metallic state during the incorporation and pyrolysis of therhenium carbonyl component, of a tin component, and of a halogencomponent. The present invention uses a dual-function catalyst havingboth a hydrogenation-dehydrogenation function and a cracking functionwhich affords substantial improvements in hydrocarbon isomerizationprocesses that have traditionally used dual-function catalysts.

Processes for the isomerization of hydrocarbons have aquired significantimportance within the petrochemical and petroleum refining industry. Thedemand for para-xylene has created a demand for processes to isomerizeother xylene isomers and ehtylbenzene to produce para-xylene. The demandfor certain branched chain paraffins, such as isobutane or isopentane,as intermediates in producing high octane motor fuel alkylate, can bemet by isomerizing the corresponding normal paraffins. It is desiredthat the alkylate be highly branched to provide a high octane rating.This can be accomplished by alkylating an isoparaffin with C₄ -C₇internal olefins which, in turn, can be produced by isomerization ofcorresponding linear alpha-olefins.

Catalytic composites exhibiting a dual hydrogenation-dehydrogenation andcracking function are widely used in the petroleum and petrochemicalindustry to isomerize hydrocarbons. Such catalysts generally have aheavy metal component, e.g., metals or metallic compounds of Groups Vthrough VIII of the Periodic Table, to impart ahydrogenation-dehydrogenation function, with an acid-acting inorganicoxide to impart a cracking function. In catalysis of isomerizationreactions, it is important that the catalytic composite not onlycatalyze the specific desired isomerization reaction by having its dualhydrogenation-dehydrogenation function correctly balanced against itscracking function, but also that the catalyst perform its desiredfunctions well over prolonged periods of time.

The performance of a given catalyst in a hydrocarbon isomerizationprocess is typically measured by the activity, selectivity, andstability of the catalyst. Activity refers to the ability of a catalystto isomerize the hydrocarbon reactants into the corresponding isomers ata specified set of reaction conditions; selectivity refers to thepercent of reactants isomerized to form the desired isomerized productand/or products; stability refers to the rate of change of theselectivity and activity of the catalyst.

The principal cause of instability (i.e., loss of selectivity andactivity in an originally selective, active catalyst) is the formationof coke on the catalytic surface of the catalyst during the reaction.This coke is characterizable as a high molecular weight,hydrogen-deficient, carbonaceous material, typically having an atomiccarbon to hydrogen ratio of about 1 or more. Thus, a problem in thehydrocarbon isomerization art is the development of more active andselective composites not sensitive to the carbonaceous materials and/orhaving the ability to suppress the rate of formation of thesecarbonaceous materials on the catalyst. A primary aim of the art is todevelop a hydrocarbon isomerization process utilizing a dual-functioncatalyst having superior activity, selectivity and stability. Inparticular, it is desired to provide a process wherein hydrocarbons areisomerized without excess cracking or other decomposition reactionswhich lower the overall yield of the process and make it more difficultto operate.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a process for isomerizingisomerizable hydrocarbons. It is another object of this invention toprovide an isomerization process using a particular isomerizationcatalyst effective in isomerizing isomerizable hydrocarbons withoutintroducing undesired decomposition and/or cracking reactions. It is afurther object of this invention to provide a process for isomerizingisomerizable hydrocarbons utilizing a dual-function catalyst havingsuperior activity, selectivity and stability.

It is also an object of the present invention to provide an improvedisomerization catalyst.

Accordingly, the present invention provides a catalyst comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, which is maintained in the elemental metallic state duringthe incorporation and pyrolysis of the rhenium carbonyl component, of atin component, of a halogen component and of about 1 to about 100 wt.%of a Friedel-Crafts metal halide calculated on a Friedel-Crafts metalhalide free basis.

In another embodiment, the present invention provides a process forisomerizing an isomerizable hydrocarbon which comprises contacting saidhydrocarbon at isomerization conditions with a catalyst comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, which is maintained in the elemental metallic state duringthe incorporation and pyrolysis of the rhenium carbonyl component, of atin component, and of a halogen component.

DETAILED DESCRIPTION

The process of this invention is applicable to the isomerization ofisomerizable saturated hydrocarbons including acyclic paraffins andnaphthenes and is particularly suitable for the isomerization ofstraight chain or mildly branched chain paraffins containing 4 or morecarbon atoms per molecule such as normal butane, normal pentane, normalhexane, normal heptane, normal octane, etc., and mixtures thereof.Cycloparaffins applicable are those containing at least 5 carbon atomsin the ring such as alkylcyclopentanes and cyclohexanes, includingmethylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, etc. This process also appliesto the conversion of mixtures of paraffins and/or naphthenes such asthose derived by selective fractionation and distillation ofstraight-run natural gasolines and naphthas. Such mixtures of paraffinsand/or naphthenes include the so-called pentane fractions, hexanefractions and mixtures thereof. It is not intended, however, to limitthis invention to these enumerated saturated hydrocarbons and it iscontemplated that straight or branched chain saturated hydrocarbons andnaphthenes containing up to about 20 carbon atoms per molecule may beisomerized according to the process of the present invention with C₄ -C₉acyclic saturated hydrocarbons and C₅ -C₉ cycloparaffins beingparticularly preferred.

The olefins applicable within this isomerization process are generally amixture of olefinic hydrocarbons of approximately the same molecularweight, including the 1-isomer, 2-isomer and other position isomers,capable of undergoing isomerization to an olefin in which the doublebond occupies a different position in the hydrocarbon chain. The processof this invention can be used to provide an olefinic feedstock for motorfuel alkylation purposes containing an optimum amount of the morecentrally located double bond isomers, by converting the 1-isomer, orother near-terminal-position isomer into olefins wherein the double bondis more centrally located in the carbon atom chain. The process of thisinvention is applicable to the isomerization of such isomerizableolefinic hydrocarbons as 1-butene to 2-butene or 3-methyl-1-butene to2-methyl-2-butene. The process of this invention can be utilized toshift the double bond of an olefinic hydrocarbon such as 1-pentene,1-hexene, 2-hexene, or 4-methyl-1-pentane to a more centrally locatedposition so that 2-pentene, 2-hexene, 3-hexene or 4-methyl-2-pentene,respectively, can be obtained. It is not intended to limit thisinvention to the enumerated olefinic hydrocarbons. It is contemplatedthat shifting the double bond to a different position may be effectivein straight or branched chain olefinic hydrocarbons containing from 4 upto about 20 carbon atoms per molecule. The process of this inventionalso applies to the hydroisomerization of olefins wherein olefins areconverted to branched-chain paraffins and/or branched olefins.

The process of this invention is also applicable to the isomerization ofisomerizable alkylaromatic hydrocarbons, e.g., ortho-xylene,meta-xylene, para-xylene, ethylbenzene, the ethyltoluenes, thetrimethylbenzenes, the diethylbenzenes, the triethylbenzenes, normalpropylbenzene, isopropylbenzene, etc., and mixtures thereof. Preferredisomerizable alkylaromatic hydrocarbons are the alkylbenzenehydrocarbons, particularly the C₈ alkylbenzenes, and non-equilibriummixtures of various C₈ aromatic isomers. Higher molecular weightalkylaromatic hydrocarbons such as the alkylnaphthalenes, thealkylanthracenes, the alkylphenanthrenes, etc., are also suitable.

The isomerizable hydrocarbons may be utilized as found in selectivefractions from various naturally-occurring petroleum streams, e.g., asindividual components or as certain boiling range fractions obtained bythe selective fractionation and distillation of catalytically crackedgas oil. The process of this invention may be utilized for completeconversion of isomerizable hydrocarbons when they are present in minorquantities in various fluid or gaseous streams. The isomerizablehydrocarbons for use in the process of this invention need not beconcentrated. For example, isomerizable hydrocarbons appear in minorquantities in various refinery offstreams, usually diluted with gasessuch as hydrogen, nitrogen, methane, ethane, propane, etc. Theseoffstreams, containing minor quantities of isomerizable hydrocarbons,are obtained from various refinery installations, including thermalcracking units, catalytic cracking units, thermal reforming units,coking units, polymerization units, dehydrogenation units, etc., andhave in the past been burned as fuel, since an economical process forthe utilization of the hydrocarbon content has not been available. Thisis particularly true of refinery fluid streams which contain minorquantities of isomerizable hydrocarbons. The process of this inventionallows the isomerization of aromatic streams since as reformate toproduce xylenes, particularly paraxylene, thus upgrading the reformatefrom its gasoline value to a high petrochemical value.

As hereinbefore indicated, the catalyst utilized in the process of thepresent invention comprises a combination of a catalytically effectiveamount of a pyrolyzed rhenium carbonyl component with a porous carriermaterial containing a uniform dispersion of catalytically effectiveamounts of a platinum group component, which is maintained in theelemental metallic state during the incorporation and pyrolysis of therhenium carbonyl component, of a tin component, and of a halogencomponent.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the isomerization process, and it is intendedto include within the scope of the present invention carrier materialswhich have traditionally been utilized in dual-function hydrocarbonconversion catalysts such as: (1) activated carbon, coke or charcoal;(2) silica or silica gel, silicon carbide, clays and silicates includingthose synthetically prepared and naturally occurring, which may or maynot be acid treated, for example, attapulgus clay, china clay,diatomaceous earth, fuller's earth, kaolin, kieselguhr, etc.; (3)ceramics porcelain, crushed firebrick, bauxite; (4) refractory inorganicoxides such as alumina, titanium dioxide, zirconium dioxide, chromiumoxide, beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide,zinc oxide, magnesia, boria, thoria, silica-alumina, silica-magnesia,chromia-alumina, alumina-boria, silica-zirconia, etc.; (5) crystallinezeolitic aluminosilicates such as naturally occurring or syntheticallyprepared mordenite and/or faujasite, either in the hydrogen form or in aform which has been treated with multivalent cations; (6) spinels suchas MgAl₂ O₄, FeAl₂ O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄ and other likecompounds having the formula MO·Al₂ O₃, where M is a metal having avalence of 2; and, (7) combinations of elements from one or more ofthese groups. The preferred porous carrier materials for use in thepresent invention are refractory inorganic oxides, with best resultsobtained with an alumina carrier material. Suitable alumina materialsare the crystalline aluminas known as gamma-, eta-, and theta-alumina,with gamma- or eta-alumina giving best results. In addition, in someembodiments the alumina carrier material may contain minor proportionsof other well-known refractory inorganic oxides such as silica,zirconia, magnesia, etc.; however, the preferred support issubstantially pure gamma- or eta-alumina. Preferred carrier materialshave an apparent bulk density of about 0.3 to about 0.7 g/cc and surfacearea characteristics such that the average pore diameter is about 20 to300 Angstroms, the pore volume is about 0.1 to about 1 cc/g and thesurface area is about 100 to about 500 m² /g. In general, best resultsare typically obtained with a gamma-alumina carrier material which isused in the form of spherical particles having: a relatively smalldiameter (i.e., typically about 1/16-inch), an apparent bulk density ofabout 0.3 to about 0.8 g/cc, a pore volume of about 0.4 ml/g and asurface area of about 200 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such anammonia hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere; and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. This treatment effects conversion of the aluminahydrogen to the corresponding crystalline gamma-alumina. See theteachings of U.S. Pat. No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersible product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing agent and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. A preferred type of carrier material for the present invention is acylindrical extrudate having a diameter of about 1/32" to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with an L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt.%, with a value of about 55 wt.% being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt.% of the volatile free alumina powder used in the mix,with a value of about 3 to 4 wt.% being especially preferred. Theresulting dough is then extruded through a suitably sized die to formextrudate particles. These particles are then dried at a temperature ofabout 500° F. to 800° F. for a period of about 0.1 to about 5 hours andthereafter calcined at a temperature of about 900° F. to about 1500° F.for a period of about 0.5 to about 5 hours to form the preferredextrudate particles of the Ziegler alumina carrier material. Inaddition, in some embodiments of the present invention the Ziegleralumina carrier material may contain minor proportions of otherwell-known refractory inorganic oxides such as silica, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, iron oxide, cobalt oxide,magnesia, boria, thoria, and the like materials which can be blendedinto the extrudable dough prior to the extrusion of same. In the samemanner crystalline zeolitic aluminosilicates such as naturally occurringor synthetically prepared mordenite and/or faujasite, either in thehydrogen form or in a form which has been treated with a multivalentcation, such as a rare earth, can be incorporated into this carriermaterial by blending finely divided particles of same into theextrudable dough prior to extrusion of same. A preferred carriermaterial of this type is substantially pure Ziegler alumina having anapparent bulk density (ABD) of about 0.6 to 1 g/cc (especially an ABD ofabout 0.7 to about 0.85 g/cc), a surface area (B.E.T.) of about 150 toabout 280 m² /g (preferably about 185 to about 235 m² /g) and a porevolume (B.E.T.) of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the attenuated superactive catalytic composite. It isan essential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt.% of the finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt.% ofplatinum, iridium, rhodium, palladium or ruthenium metal. Particularlypreferred mixtures of these platinum group metals preferred for use inthe composite of the present invention are: (1) platinum and iridium,(2) platinum and rhodium, and (3) platinum and ruthenium.

This platinum group component may be incorporated into the porouscarrier material in any suitable manner known to result in a relativelyuniform distribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of platinum, iridium, rhodium, orpalladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentand at least a minor quantity of the preferred halogen component in asingle step. Hydrogen chloride or the like acid is also generally addedto the impregnation solution in order to further facilitate theincorporation of the halogen component and the uniform distribution ofthe metallic components throughout the carrier material. In addition, itis generally preferred to impregnate the carrier material after it hasbeen calcined in order to minimize the risk of washing away the valuableplatinum group compound.

A second essential constituent of the multimetallic catalyst of thepresent invention is a tin component. This component may in general bepresent in the instant catalytic composite in any catalyticallyavailable form such as the elemental metal, a compound like the oxide,hydroxide, halide, oxyhalide, aluminate, or in chemical combination withone or more of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation, it isbelieved that best results are obtained when the tin component ispresent in the composite in a form wherein substantially all of the tinmoiety is in an oxidation state above that of the elemental metal suchas in the form of tin oxide or tin halide or tin oxyhalide or a mixturethereof and the subsequently described oxidation and reduction stepsthat are preferably used in the preparation of the instant catalyticcomposite are specifically designed to achieve this end. The term"tin-oxyhalide" as used herein refers to a coordinated complex of tin,oxygen and halogen which are not necessarily present in the samerelationship for all cases covered herein. This tin component can beused in any amount which is catalytically effective, with good resultsobtained, on an elemental basis, with about 0.005 to about 5 wt.% tin inthe catalyst. Best results are ordinarily achieved with about 0.01 toabout 1 wt.% tin, calculated on an elemental basis. The preferred atomicratio of tin to platinum group metal for this catalyst is about 0.1:1 toabout 13:1.

This tin component may be incorporated in the catalytic composite in anysuitable manner known to the art to result in a relatively uniformdispersion of the tin moiety in the carrier material, such as bycoprecipitation or cogelation or coextrusion with the porous carriermaterial, ion exchange with the gelled carrier material, or impregnationof the porous carrier material either after, before, or during theperiod when it is dried and calcined. It is to be noted that it isintended to include within the scope of the present invention allconventional methods for incorporating and simultaneously uniformlydistributing a metallic component in a catalytic composite and theparticular method of incorporation used is not deemed to be an essentialfeature of the present invention. One particularly preferred method ofincorporating the tin component into the catalytic composite involvescogelling or coprecipitating the tin component in the form of thecorresponding hydrous oxide during the preparation of the preferredcarrier material, alumina. This method typically involves the additionof a suitable sol-soluble or sol-dispersible tin compound such asstannic or stannous chloride, tin acetate, and the like to the aluminahydrosol, thoroughly mixing the resulting tin-containing hydrosol inorder to uniformly disperse the tin moiety throughout the sol, and thencombining the tin-containing hydrosol with a suitable gelling agent anddropping the resulting mixture into an oil bath, etc., as explained indetail hereinbefore. Alternatively, the tin compound can be added to thegelling agent. After drying and calcining the resulting gelled carriermaterial in air, there is obtained an intimate combination of aluminaand tin oxide and/or oxyhalide. A second preferred method ofincorporating the tin component into the catalytic composite involvesutilization of a soluble, decomposable compound of tin to impregnate theporous carrier material. In general, the solvent used in thisimpregnation step is selected on the basis of the capability to dissolvethe desired tin compound and to hold it in solution until it is evenlydistributed throughout the carrier material without adversely affectingthe carrier material or the other ingredients of the catalyst--forexample, a suitable alcohol, ether, acid and the like solvents. Thesolvent is preferably an aqueous, acidic solution. The tin component maythus be added to the carrier material by commingling the latter with anaqueous acidic solution of suitable tin salt, complex, or compound suchas stannic acetate, stannous or stannic bromide, stannous or stannicchloride, stannic chloride pentahydrate, stannic chloride diamine,stannic trichloride bromide, stannic chromate, stannous or stannicfluoride, stannic tartrate, dimethyltin dibromide, dimethyltindichloride, ethylpropyltin dichloride, triethyltin hydroxide,trimethyltin chloride, and the like compounds. A particularly preferredimpregnation solution comprises an acidic aqueous solution of stannic orstannous chloride. Suitable acids for use in the impregnation solutionare: inorganic acids such as hydrochloric acid, nitric acid, and thelike, and strongly acidic organic acids such as oxalic acid, malonicacid, citric acid, and the like. In general, the tin component can beimpregnated either prior to, simultaneously with, or after the platinumgroup component is added to the carrier material. However, excellentresults are obtained when the tin component is incorporated into thecarrier material during its preparation and thereafter the platinumgroup component is added in a subsequent impregnation step after thetin-containing carrier material is calcined. A third preferred method ofadding the tin component is to select a rhenium-carbonyl complex thatalso contains a tin ligand in the subsequently describedrhenium-carbonyl incorporation step, thereby adding the tin componentsimultaneously with the rhenium-carbonyl component.

It is especially preferred to incorporate a halogen component into theplatinum group metal-containing porous carrier material prior to thereactions thereof with the rhenium carbonyl reagent. Although theprecise form of the chemistry of the association of the halogencomponent with the catalytic composite is not entirely known, it iscustomary in the art to refer to the halogen component as beingchemically combined with the carrier material or with the platinum groupand/or tin components in the form of the halide (e.g. as the chloride).This combined halogen may be either fluorine, chlorine, iodine, bromide,or mixtures thereof. Of these, fluorine and, particularly, chlorine arepreferred for the purposes of the present invention. The halogen may beadded to the carrier material in any suitable manner, either duringpreparation of the support or before or during or after the addition ofthe platinum group and tin components. For example, the halogen may beadded, at any stage of the preparation of the carrier material or to thecalcined carrier material, as an aqueous solution of a suitable,decomposable halogen-containing compound such as hydrogen fluoride,hydrogen chloride, hydrogen bromide, ammonium chloride, etc. The halogencomponent or a portion thereof, may be combined with the carriermaterial during the impregnation of the latter with the platinum groupand/or tin components, for example, through the utilization of a mixtureof chloroplatinic acid and hydrogen chloride. In another situation, thealumina hydrosol which is typically utilized to form a preferred aluminacarrier material may contain halogen and thus contribute at least aportion of the halogen component to the final composite. For reforming,the halogen will be typically combined with the carrier material in anamount sufficient to result in a final composite that contains about 0.1to about 3.5%, and preferably about 0.5 to about 1.5%, by weight ofhalogen, calculated on an elemental basis. In isomerization orhydrocracking embodiments, it is generally preferred to utilizerelatively larger amounts of halogen in the catalyst--typically, rangingup to about 10 wt.% halogen calculated on an elemental basis, and morepreferably, about 1 to about 5 wt.%. It is to be understood that thespecified level of halogen component in the instant attenuatedsuperactive catalyst can be achieved or maintained during use in theconversion of hydrocarbons by continuously or periodically adding to thereaction zone a decomposable halogen-containing compound such as anorganic chloride (e.g. ethylene dichloride, carbon tetrachloride,t-butyl chloride) in an amount of about 1 to 100 wt. ppm. of thehydrocarbon feed, and preferably about 1 to 10 wt. ppm.

After the tin components (when added prior to the rhenium carbonylincorporation step) and platinum group components are combined with theporous carrier material, the resulting platinum group metal- andtin-containing carrier material will generally be dried at a temperatureof about 200° F. to about 600° F. for a period of typically about 1 toabout 24 hours or more and thereafter oxidized at a temperature of about700° F. to about 1100° F. in an air or oxygen atmosphere for a period ofabout 0.5 to about 10 or more hours or converts substantially all of theplatinum group and tin components to the corresponding metallic oxides.When the preferred halogen component is utilized in the presentcomposition, best results are generally obtained when the halogencontent of the platinum group metal- and tin-containing carrier materialis adjusted during this oxidation step by including a halogen or ahalogen-containing compound in the air or oxygen atmosphere utilized.For purposes of the present invention, the particularly preferredhalogen is chlorine and it is highly recommended that the halogencompound utilized in this halogenation step be either hydrochloric acidor a hydrochloric acid-producing substance. In particular, when thehalogen component of the catalyst is chlorine, it is preferred to use amolar ratio of H₂ O to HCl of about 5:1 to about 100:1 during at least aportion of this oxidation step in order to adjust the final chlorinecontent of the catalyst to a range of about 0.1 to about 3.5 wt.%.Preferably, the duration of this halogenation step is about 1 to 5 ormore hours.

A crucial feature of the present invention involves subjecting theresulting oxidized, tin-containing (when added prior to the rheniumcarbonyl incorporation step) and platinum group metal-containing, andtypically halogen-treated, carrier material to a substantiallywater-free reduction step before the incorporation of the rheniumcomponent by means of the rhenium carbonyl reagent. The importance ofthis reduction step comes from my observation that when an attempt ismade to prepare the instant catalytic composite without first reducingthe platinum group component, no significant improvement in theplatinum-rhenium-tin catalyst system is obtained; put another way, it ismy finding that it is essential for the platinum group component to bewell dispersed in the porous carrier material in the elemental metallicstate prior to incorporation of the rhenium component by the uniqueprocedure of the present invention in order for synergistic interactionof the rhenium carbonyl with the dispersed platinum group metal to occuraccording to the theories that I have previously explained. Accordingly,this reduction step is designed to reduce substantially all of theplatinum group component to the elemental metallic state and to assure arelatively uniform and finely divided dispersion of this metalliccomponent throughout the porous carrier material. Preferably asubstantially pure and dry hydrogen stream (by the use of the word"dry", I mean that it contains less than 20 vol. ppm. water andpreferably less than 5 vol. ppm. water) is used as the reducing agent inthis step. The reducing agent is contacted with the oxidized, platinumgroup metal- and tin-containing carrier material at conditions includinga reduction temperature of about 450° F. to about 1200° F., a gas hourlyspace velocity (GHSV) sufficient to rapidly dissipate any localconcentrations of water formed during the reduction of the platinumgroup metal oxide, and a period of about 0.5 to about 10 or more hoursselected to reduce substantially all of the platinum group component tothe elemental metallic state. Once this condition of finely divideddispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A third essential ingredient of the present attenuated superactivecatalytic composite is a rhenium component which I have chosen tocharacterize as a pyrolyzed rhenium carbonyl component in order toemphasize that the rhenium moiety of interest in my invention is therhenium produced by decomposing a rhenium carbonyl in the presence of afinely divided dispersion of a platinum group metal and in the absenceof materials such as oxygen or water which could interfere with thebasic desired interaction of the rhenium carbonyl component with theplatinum group metal component as previously explained. In view of thefact that all of the rhenium contained in a rhenium carbonyl complex ispresent in the elemental metallic state, an essential requirement of myinvention is that the resulting reaction product of the rhenium carbonylcomplex with the platinum group metal-containing carrier material is notsubjected to conditions which could in any way interfere with themaintenance of the rhenium moiety in the elemental metallic state;consequently, avoidance of any conditions which would tend to cause theoxidation of any portion of the rhenium ingredient or of the platinumgroup ingredient is a requirement for full realization of thesynergistic interaction enabled by the present invention. This rheniumcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 5 wt.% thereof, calculated on anelemental rhenium basis. Best results are ordinarily obtained with about0.05 to about 1 wt.% rhenium. The traditional rule for rhenium-platinumcatalyst system is that best results are achieved when the amount of therhenium component is set as a function of the amount of the platinumgroup component also hold for my composition; specifically, I find thatbest results with a rhenium to platinum group metal atomic ratio ofabout 0.1:1 to about 10:1, with an especially useful range comprisingabout 0.2:1 to about 5:1 and with superior results achieved at an atomicratio of rhenium to platinum group metal of about 1:1 to about 3:1.

The rhenium carbonyl ingredient may be reacted with the reduced platinumgroup metal-containing porous carrier material in any suitable mannerknown to those skilled in the catalyst formulation art which results inrelatively good contact between the rhenium carbonyl complex and theplatinum group component contained in the porous carrier material. Oneacceptable procedure for incorporating the rhenium carbonyl componentinto the composite involves sublimating the rhenium carbonyl complexunder conditions which enable it to pass into the vapor phase withoutbeing decomposed and thereafter contacting the resulting rheniumcarbonyl sublimate with the platinum group metal-containing porouscarrier material under conditions designed to achieve intimate contactof the carbonyl reagent with the platinum group metal dispersed on thecarrier material. Typically this procedure is performed under vacuum ata temperature of about 70° F. to about 250° F. for a period of timesufficient to react the desired amount of rhenium with the carriermaterial. In some cases, an inert carrier gas such as nitrogen can beadmixed with the rhenium carbonyl sublimate in order to facilitate theintimate contacting of same with the platinum group metal-loaded porouscarrier material. A particularly preferred way of accomplishing thisrhenium carbonyl reaction step is an impregnation procedure wherein theplatinum group metal-containing porous carrier material is impregnatedwith a suitable solution containing the desired quantity of the rheniumcarbonyl complex. For purposes of the present invention, organicsolutions are preferred, although any suitable solution may be utilizedas long as it does not interact with the rhenium carbonyl and causedecomposition of same. Obviously, the organic solution should beanhydrous in order to avoid detrimental interaction of water with therhenium carbonyl complex. Suitable solvents are any of the commonlyavailable organic solvents such as one of the available ethers,alcohols, ketones, aldehydes, paraffins, naphthenes and aromatichydrocarbons, for example, acetone, acetyl acetone, benzaldehyde,pentane, hexane, carbon tetrachloride, methyl isopropyl ketone, benzene,n-butylether, diethyl ether, ethylene glycol, methyl isobutyl ketone,diisobutyl ketone and the like organic solvents. Best results areordinarily obtained when the solvent is acetone; consequently, thepreferred impregnation solution is rhenium carbonyl dissolved inanhydrous acetone. The rhenium carbonyl complex suitable for use in thepresent invention may be either the pure rhenium carbonyl itself or asubstituted rhenium carbonyl such as the tin-containing complexes likeClSn[Re(CO)₅ ]₃ mentioned previously or the rhenium carbonyl halidesincluding the chlorides, bromides and iodides and the like substitutedrhenium carbonyl complexes. After impregnation of the carrier materialwith the rhenium carbonyl component, it is important that the solvent beremoved or evaporated from the catalyst prior to decomposition of therhenium carbonyl component by means of the hereinafter describedpyrolysis step. The reason for removal of the solvent is that I believethat the presence of organic materials such as hydrocarbons orderivatives of hydrocarbons during the rhenium carbonyl pyrolysis stepis highly detrimental to the synergistic interaction associated with thepresent invention. This solvent is removed by subjecting the rheniumcarbonyl impregnated carrier material to a temperature of about 100° F.to about 250 ° F. in the presence of an inert gas or under a vacuumcondition until no further substantial amount of solvent is observed tocome off the impregnated material. In the preferred case where acetoneis used as the impregnation solvent, this drying of the impregnatedcarrier material typically takes about one half hour at a temperature ofabout 225° F. under moderate vacuum conditions.

After the rhenium carbonyl component is incorporated into the platinumgroup metal-containing porous carrier material, the resulting compositeis, pursuant to the present invention, subjected to pyrolysis conditionsdesigned to decompose substantially all of the rhenium carbonylmaterial, without oxidizing either the platinum group component or thedecomposed rhenium carbonyl component. This step is preferably conductedin an atmosphere which is substantially inert to the rhenium carbonylsuch as in a nitrogen or noble gas-containing atmosphere. Preferablythis pyrolysis step takes place in the presence of a substantially pureand dry hydrogen stream. It is of course within the scope of the presentinvention to conduct the pyrolysis step under vacuum conditions. It ismuch preferred to conduct this step in the substantial absence of freeoxygen and substances that could yield free oxygen under the conditionsselected. Likewise it is clear that best results are obtained when thisstep is performed in the total absence of water and of hydrocarbons andother organic materials. I have obtained best results in pyrolyzingrhenium carbonyl while using an anhydrous hydrogen stream at pyrolysisconditions including a temperature of about 300° F. to about 900° F. ormore, preferably about 400° F. to about 750° F., a gas hourly spacevelocity of about 250 to about 1500 hr.⁻¹ for a period of about 0.5 toabout 5 or more hours until no further evolution of carbon monoxide isnoted. After the rhenium carbonyl component has been pyrolyzed, it is amuch preferred practice to maintain the resulting catalytic composite inan inert environment (i.e. a nitrogen or the like inert gas blanket)until the catalyst is loaded into a reaction zone for use in theconversion of hydrocarbons.

It is essential to incorporate a halogen component into the trimetalliccatalytic composite of the present invention. Although the precise formof the chemistry of the association of the halogen component with thecarrier material is not entirely known, it is customary in the art torefer to the halogen component as being combined with the carriermaterial, or with the other ingredients of the catalyst in the form ofthe halide (e.g., as the chloride). This combined halogen may be eitherfluorine, chlorine, iodine, bromine, or mixtures thereof. Of these,fluorine and particularly chlorine are preferred for the purposes of thepresent invention. The halogen may be added to the carrier material inany suitable manner, either during preparation of the support or beforeor after the addition of the other components. For example, the halogenmay be added, at any stage of the preparation of the carrier material orto the calcined carrier material, as an aqueous solution of a suitable,decomposable halogen-containing compound such as hydrogen fluoride,hydrogen chloride, hydrogen bromide, ammonium chloride, etc. The halogencomponent or a portion thereof, may be combined with the carriermaterial during the impregnation or incorporation of the latter with theplatinum group metal and tin components, for example, through theutilization of a mixture of chloroplatinic acid and hydrogen chloride.In another situation, the alumina hydrosol which is typically utilizedto form a preferred alumina carrier material may contain halogen andthus contribute at least a portion of the halogen component to the finalcomposite. The halogen will be typically combined with the carriermaterial in an amount sufficient to result in a final composite thatcontains about 0.1 to about 10% and preferably about 1 to about 5%, byweight, of halogen, calculated on an elemental basis. It is to beunderstood that the specified level of halogen component in the instantcatalyst can be achieved or maintained during use in the presentisomerization process by continuously or periodically adding to thereaction zone a decomposable halogen-containing compound such as anorganic chloride (e.g., ethylene dichloride, carbon tetrachloride,t-butyl chloride) in an amount of about 1 to 100 wt. ppm. of thehydrocarbon feed, and preferably about 1 to 10 wt. ppm.

An optional ingredient for the attenuated superactive multimetalliccatalyst of the present invention is a Friedel-Crafts metal halidecomponent. This ingredient is particularly useful in hydrocarbonconversion embodiments of the present invention wherein it is preferredthat the catalyst utilized has a strong acid or cracking functionassociated therewith--for example, an embodiment wherein thehydrocarbons are to be hydrocracked or isomerized with the catalyst ofthe present invention. Suitable metal halides of the Friedel-Crafts typeinclude aluminum chloride, aluminum bromide, ferric chloride, ferricbromide, zinc chloride, and the like compounds, with the aluminumhalides and particularly aluminum chloride ordinarily yielding bestresults. Generally, this optional ingredient can be incorporated intothe composite of the present invention by any of the conventionalmethods for adding metallic halides of this type and either prior to orafter the rhenium carbonyl reagent is added thereto; however, bestresults are ordinarily obtained when the metallic halide is sublimedonto the surface of the carrier material after the rhenium is addedthereto according to the preferred method disclosed in U.S. Pat. No.2,999,074. The component can generally be utilized in any amount whichis catalytically effective, with a value selected from the range ofabout 1 to about 100 wt.% of the carrier material generally beingpreferred.

In the preferred method, wherein the catalytic composite is impregnatedwith a Friedel-Crafts metal halide component, the presence of chemicallycombined hydroxyl groups in the refractory inorganic oxide allows areaction to occur between the Friedel-Crafts metal halide and thehydroxyl group of the carrier material. For example, aluminum chloridereacts with the hydroxyl groups of the preferred alumina carriermaterial to yield Al-O-AlCl₂ active centers which enhance the catalyticbehavior of the composite. Since chloride ions and hydroxyl ions occupysimilar sites on the carrier surface, more hydroxyl sites will beavailable for possible interaction with the Friedel-Crafts metal halidewhen the chloride population of the carrier sites is low. Therefore,potentially more active Friedel-Crafts type versions of the catalystwill be obtained when the chloride content of the carrier material is inthe low range of the 0.1 to 10 wt.% range. Some halogen must be presenton the carrier material at all times, however, to maintain properdispersion of the other active elements.

The Friedel-Crafts metal halide may be impregnated onto the calcinedcomposite containing combined hydroxyl groups by the sublimation of theFriedel-Crafts metal halide onto the calcined composite under conditionssuch that the sublimed Friedel-Crafts metal halide is combined with thehydroxyl groups of the calcined composite. This reaction is typicallyaccompanied by the elimination of about 0.5 to about 2.0 moles ofhydrogen chloride per mole of Friedel-Crafts metal halide reacted withthe carrier material. For example, in the case of subliming aluminumchloride, which sublimes at about 184° C., suitable impregnationtemperatures range from about 190° C. to about 700° C., with apreferably range being between about 200° C. and about 600° C. In anyevent, the sublimation temperature must be selected so as to precludethe alteration of the oxidation states of metal components. Thesublimation can be conducted at atmospheric pressure or under increasedpressure and in the presence or absence of diluent gases such ashydrogen or light paraffinic hydrocarbons or both. The impregnation ofthe Friedel-Crafts metal halide may be conducted batch wise, but apreferred method for impregnating the calcined composite is to passsublimed AlCl₃ vapors, in admixture with a carrier gas such as hydrogen,through a catalyst bed. This method both continuously deposits andreacts the aluminum chloride and also removes the evolved HCl.

The amount of Friedel-Crafts metal halide combined with the catalyticcomposite may range from about 1 wt.% up to about 100 wt.% of theFriedel-Crafts metal halide-free, catalytic composite as abovementioned.The final composite containing the sublimed Friedel-Crafts metal halideis treated to remove the unreacted Friedel-Crafts metal halide bysubjecting the composite to a temperature above the sublimationtemperature of the Friedel-Crafts metal halide for a time sufficient toremove from the composite any unreacted Friedel-Crafts metal halide. Inthe case of AlCl₃, temperatures of about 400° C. to about 600° C., andtimes of from about 1 to about 48 hours are sufficient.

The resulting catalytic composite is preferably maintained in asulfur-free state during its preparation and use. Once the catalyst hasbeen exposed to hydrocarbon for a sufficient period of time to lay downa protective layer of carbon or coke on the catalyst, the sulfursensitivity of the catalyst changes rather markedly and the presence ofsmall amounts of sulfur can be tolerated. Thus, contact of freshcatalyst with sulfur can seriously damage the catalyst and jeopardizethe superior performance characteristics of the catalyst. However, oncea protective layer of carbon is established on the catalyst, the sulfurdeactivation effect is less permanent and the sulfur can be purged fromthe catalyst by exposure to a sulfur-free hydrogen stream at 425° C. to460° C.

According to the process of the present invention, an isomerizablehydrocarbon charge stock, preferably in admixture with hydrogen, iscontacted with a catalyst of the type hereinbefore described in ahydrocarbon isomerization zone. Contacting may be effected using thecatalyst in a fixed bed system, a moving bed system, a fluidized bedsystem, or in a batch type operation. In view of the danger of attritionloss of the valuable catalyst and of operational advantages, it ispreferred to use a fixed bed system. In this system, a hydrogen-rich gasand the charge stock are preheated by suitable heating means to thedesired reaction temperature and then passed into an isomerization zonecontaining a fixed bed of the catalyst type previously characterized.The conversion zone may be one or more separate reactors with suitablemeans therebetween to insure that the desired isomerization temperatureis maintained at the entrance to each zone. It is to be noted that thereactants may be contacted with the catalyst bed in either upward,downward, or radial flow fashion, and that the reactants may be in theliquid phase, a mixed liquid-vapor phase, or a vapor phase whencontacted with the catalyst, with best results obtained in a vaporphase.

The process of this invention, utilizing the catalyst described abovefor isomerizing isomerizable olefinic or saturated hydrocarbons, ispreferably effected in a continuous down-flow fixed bed system. Onepreferred method is to pass the hydrocarbons continuously, preferablycommingled with about 0.1 to about 10 moles or more of hydrogen per moleof hydrocarbon, to an isomerization reaction zone containing thecatalyst, and to maintain the zone at proper isomerization conditionssuch as a temperature in the range of about 0° C. to about 425° C. ormore and a pressure of about atmospheric to about 100 atmospheres ormore. The hydrocarbon is passed over the catalyst at a liquid hourlyspace velocity (defined as volume of liquid hydrocarbon passed per hourper volume of catalyst) of from about 0.1 to about 10 hr.⁻¹ or more. Inaddition, diluents such as argon, nitrogen, etc., may be present. Theisomerized product is continuously withdrawn, separated from the reactoreffluent, and recovered by conventional means such as fractionaldistillation, while the unreacted starting material may be recycled toform a portion of the feedstock.

The process of this invention for isomerizing an isomerizablealkylaromatic hydrocarbon is preferably effected by contacting thealkylaromatic, in a reaction zone containing the hereinbefore describedcatalyst, with a fixed catalyst bed by passing the hydrocarbon in adown-flow fashion through the bed, while maintaining the zone at properalkylaromatic isomerization conditions such as a temperature in therange from about 0° C. to about 600° C. or more, and a pressure ofatomspheric to about 100 atmospheres or more. The hydrocarbon is passed,preferably, in admixture with hydrogen at a hydrogen to hydrocarbon moleratio of about 0.5:1 to about 20:1 or more, and at a liquid hourlyhydrocarbon space velocity of about 0.1 to about 20 hr.⁻¹ or more. Otherinert diluents such as nitrogen, argon, etc., may be present. Theisomerized product is continuously withdrawn, separated from the reactoreffluent by conventional means including fractional distillation orcrystallization, and recovered.

The following illustrative embodiments are given to illustrate furtherthe preparation of the multimetallic catalytic composite utilized in theprocess of the present invention and the employment of the catalyst inisomerization of hydrocarbons. It is to be understood that the examplesare illustrative rather than restrictive.

ILLUSTRATIVE EMBODIMENT I

This example demonstrates a particularly good method of preparing thepreferred catalytic composite utilized in the process of the presentinvention.

A sulfur-free tin- and chloride-containing alumina carrier materialcomprising 1/16-inch spheres was prepared by: forming an aluminumhydroxy chloride sol by dissolving substantially pure aluminum pelletsin a hydrochloric acid solution, thoroughly mixing stannic chloride withthe resulting sol in an amount selected to result in a final catalystcontaining about 0.2 wt.% tin, adding hexamethylenetetramine to theresulting tin-containing alumina sol, gelling the resulting solution bydropping it into an oil bath to form spherical particles of atin-containing alumina hydrogel, aging and washing the resultingparticles and finally drying and calcining the aged and washed particlesto form spherical particles of gamma-alumina having a tin componentuniformly dispersed therein and containing, on an elemental basis, about0.2 wt.% tin and about 0.3 wt.% combined chloride. Additional details asto this method of preparing the preferred gamma-alumina carrier materialare given in the teachings of U.S. Pat. No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid andhydrogen chloride was then prepared. The sulfur-free, tin-containingalumina carrier material particles were thereafter admixed with thisimpregnation solution. The amounts of the metallic reagents contained inthis impregnation solution were calculated to result in a finalcomposite containing, on an elemental basis, about 0.375 wt.% platinum.In order to insure uniform dispersion of the platinum componentthroughout the carrier material, the amount of hydrogen chloride used inthis impregnation solution was about 2 wt.% of the alumina particles.This impregnation step was performed by adding the carrier materialparticles to the impregnation mixture with constant agitation. Inaddition, the volume of the solution was approximately the same as thebulk volume of the alumina carrier material particles so that all of theparticles were immersed in the impregnation solution. The impregnationmixture was maintained in contact with the carrier material particlesfor a period of about 1/2 to about 3 hours at a temperature of about 70°F. Thereafter, the temperature of the impregnation mixture was raised toabout 225° F. and the excess solution was evaporated in a period ofabout 1 hour. The resulting dried impregnated particles were thensubjected to an oxidation treatment in a dry air stream at a temperatureof about 975° F. and a GHSV of about 500 hr.⁻¹ for about 1/2 hour. Thisoxidation step was designed to convert substantially all of the platinumand tin ingredients to the corresponding oxide forms. The resultingoxidized spheres were subsequently contacted in a halogen-treating stepwith an air stream containing H₂ O and HCl in a mole ratio of about 30:1for about 2 hours at 975° F. and a GHSV of about 500 hr.⁻¹ in order toadjust the halogen content of the catalyst particles to a value of about1 wt.%. The halogen-treated spheres were thereafter subjected to asecond oxidation step with a dry air stream at 975° F. and a GHSV of 500hr.⁻¹ for an additional period of about 1/2 hour.

The resulting oxidized, halogen-treated, platinum- and tin-containingcarrier material particles were then subjected to a dry reductiontreatment designed to reduce substantially all of the platinum componentto the elemental state and to maintain a uniform dispersion of thiscomponent in the carrier material. This reduction step was accomplishedby contacting the particles with a hydrocarbonfree, dry hydrogen streamcontaining less than 5 vol. ppm. H₂ O at a temperature of about 1050°F., a pressure slightly above atmospheric, a flow rate of hydrogenthrough the particles corresponding to a GHSV of about 400 hr.⁻¹ and fora period of about one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, was thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which was used as the vehicle for reacting rhenium carbonylwith the carrier material containing the uniformly dispersed platinumand tin. The amount of this complex used was selected to result in afinished catalyst containing about 0.375 wt.% rhenium derived fromrhenium carbonyl. The resulting rhenium carbonyl solution was thencontacted under appropriate impregnation conditions with the reduced,platinum- and tin-containing alumina carrier material resulting from thepreviously described reduction step. The impregnation conditionsutilized were: a contact time of about 1/2 to about 3 hours, atemperature of about 70° F. and a pressure of about atmospheric. It isimportant to note that this impregnation step was conducted under anitrogen blanket so that oxygen was excluded from the environment andalso this step was performed under anhydrous conditions. Thereafter theacetone solvent was removed under flowing nitrogen at a temperature ofabout 175° F. for a period of about one hour. The resulting dryrhenium-carbonyl-impregnated particles were then subjected to apyrolysis step designed to decompose the rhenium carbonyl compound. Thisstep involved subjecting the rhenium carbonyl impregnated particles to aflowing hydrogen stream at a first temperature of about 230° F. forabout 1/2 hour at a GHSV of about 600 hr.⁻¹ and at atmospheric pressure.Thereafter in the second portion of the pyrolysis step, the temperatureof the impregnated particles was raised to about 575° F. for anadditional interval of about one hour until the evolution of CO was nolonger evident. The resulting catalyst was then maintained under anitrogen blanket until it was used.

A sample of the resulting pyrolyzed rhenium-carbonyl-, tin- andplatinum-containing catalytic composite contained, on an elementalbasis, about 0.375 wt.% platinum, about 0.375 wt.% rhenium derived fromthe carbonyl, about 0.2 wt.% tin and about 1.0 wt.% chlorine. For thiscatalyst the atomic ratio of tin to platinum was about 0.88:1 and theatomic ratio of rhenium to platinum was about 1.05:1.

ILLUSTRATIVE EMBODIMENT II

A portion of the spherical multimetallic catalyst particles produced bythe method described in Illustrative Embodiment I is loaded into acontinuous, fixed bed isomerization plant of conventional design. Thecharge stock, containing on a weight percent basis, 20.0% ethylbenzene,10.0% para-xylene, 50.0% meta-xylene, and 20.0% ortho-xylene iscommingled with about 8 moles of hydrogen per mole of hydrocarbon,heated to 400° C., and continuously charged at 4.0 hr.⁻¹ liquid hourlyspace velocity (LHSV) to the reactor which is maintained at a pressureof 30 atm, absolute. The resulting product evidences essentiallyequilibrium conversion to para-xylene with only insignificant amounts ofcracked products thus indicating an efficient alkylaromaticisomerization catalyst.

ILLUSTRATIVE EMBODIMENT III

A portion of the catalyst produced by the method of IllustrativeEmbodiment I is placed in a continuous flow, fixed bed isomerizationplant of conventional design as utilized in Illustrative Embodiment II.Substantially pure meta-xylene is used as a charge stock. The chargestock is commingled with about 8 moles of hydrogen per mole ofhydrocarbon, heated to about 390° C., and continuously charged to thereactor which is maintained at a pressure of about 21 atm. Substantialconversion of meta-xylene to para-xylene is obtained.

ILLUSTRATIVE EMBODIMENT IV

A catalyst identical to that produced in Illustrative Embodiment I butcontaining only 0.40 wt.% combined chloride is used to isomerize1-butene in an appropriate isomerization reactor, at a reactor pressureof about 35 atm and a reactor temperature of about 140° C. Substantialconversion to 2-butene is observed.

ILLUSTRATIVE EMBODIMENT V

The same catalyst as utilized in Illustrative Embodiment IV is chargedto an appropriate, continuous isomerization reactor of conventionaldesign maintained at a reactor pressure of about 70 atm and a reactortemperature of about 180° C. and 3-methyl-1-butene is continuouslypassed to this reactor with substantial conversion to 2-methyl-2-butenebeing observed.

ILLUSTRATIVE EMBODIMENT VI

A catalyst, identical to that catalyst produced in IllustrativeEmbodiment I except that the gamma-alumina particles are contacted withhydrogen fluoride to provide a 2.9 wt.% combined fluoride content in thecatalyst, is placed in an appropriate continuous isomerization reactorof conventional design maintained at a reactor pressure of about 21 atmpsig. and a reactor temperature of about 200° C. Normal hexane iscontinuously charged to the reactor and substantial conversion to2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, and3-methylpentane is observed.

ILLUSTRATIVE EMBODIMENT VII

A portion of the catalyst prepared in Illustrative Embodiment I isplaced in an appropriate continuous isomerization apparatus and used toisomerize normal butane at a reactor pressure of 21 psig, a 0.5 hydrogento hydrocarbon mole ratio, a 1.0 liquid hourly space velocity, and areactor temperature of 230° C. Substantial conversion of normal butaneto isobutane is observed.

ILLUSTRATIVE EMBODIMENT VIII

A portion of the catalyst prepared in Illustrative Embodiment I isplaced in an appropriate continuous isomerization reactor maintained ata reactor temperature of about 210° C. and a reactor pressure of about18 atm. Methylcyclopentane is continuously passed to this reactor with asubstantial conversion to cyclohexane being observed.

ILLUSTRATIVE EMBODIMENT IX

A portion of the catalyst prepared in Illustrative Embodiment I isplaced in a glass lined, rotating autoclave with anhydrous aluminumchloride. Three weights of AlCl₃ are added for each four weights ofcatalyst particles. The autoclave is sealed, evacuated, then pressuredwith H₂ to 3 atm, absolute. The autoclave is heated to 300° C. for twohours, with rotation. The catalyst particles experienced a weight gainof 15 wt.%.

ILLUSTRATIVE EMBODIMENT X

Catalyst prepared in Illustrative Embodiment IX is tested forisomerization of normal butane at a 0.5 H₂ to hydrocarbon ratio, 1.0LHSV, and reactor temperature of 150° C. Substantial conversion ofnormal butane to isobutane is observed.

ILLUSTRATIVE EMBODIMENT XI

About 100 g of the catalyst prepared in Illustrative Embodiment I isplaced in a vertical Pyrex tube with a bed of 30 g of AlCl₃ on top. H₂at 250° C. and gas hourly space velocity of 250 is passed over the beduntil complete sublimation of AlCl₃ is observed. The temperature is thenincreased to 300° C. for 30 minutes. The catalyst particles are thencooled under N₂ gas flow.

ILLUSTRATIVE EMBODIMENT XII

Catalyst prepared in Illustrative Embodiment XI is tested as disclosedin Illustrative Embodiment X. Substantial conversion of normal butane toisobutane is observed.

The foregoing specification, and particularly the illustrativeembodiments indicate the method by which the present invention iseffected, and the benefits afforded through the utilization thereof.

I claim:
 1. A process for isomerizing saturated hydrocarbons whichcomprises contacting said hydrocarbon at isomerization conditions with acatalytic composite comprising a combination of a catalyticallyeffective amount of a pyrolyzed rhenium carbonyl component with a porouscarrier material containing a uniform dispersion of catalyticallyeffective amounts of a platinum group component, which is maintained inthe elemental metallic state during the incorporation and pyrolysis ofthe rhenium carbonyl component, of a tin component, and of a halogencomponent.
 2. The process of claim 1 wherein the platinum group metal isplatinum.
 3. The process of claim 1 wherein the platinum group metal ispalladium.
 4. The process of claim 1 wherein the porous carrier materialis a refractory inorganic oxide.
 5. The process of claim 4 wherein therefractory inorganic oxide is alumina.
 6. The process of claim 1 whereinthe halogen is combined chloride.
 7. The process of claim 1 containing0.01 to about 2 wt.% platinum group metal, about 0.005 to about 5 wt. %tin, about 0.01 to about 5 wt. % rhenium and about 0.5 to about 1.5 wt.% halogen.
 8. The process of claim 1 wherein the catalytic compositeadditionally contains 1 to 100 wt. % of a Friedel-Crafts metal halidebased on a Friedel-Crafts metal halide-free composite.
 9. The process ofclaim 8 wherein the Friedel-Crafts metal halide is aluminum chloride.10. The process of claim 1 wherein the isomerization conditions includea temperature of 0° to 425° C., a pressure of atmospheric to about 100atmospheres and a liquid hourly space velocity of 0.1 to
 10. 11. Theprocess of claim 1 wherein the saturated hydrocarbon is commingled with0.1 to 10 moles of hydrogen per mole of hydrocarbon.
 12. The process ofclaim 1 wherein the saturated hydrocarbon is selected from C₄ -C₉acyclic paraffins.